"It's the actual writing that's two characters more (start insert mode, write, exit)." Makes sense. Asking for permission to type in a text editor feels counter-intuitive, but I'll give that a try.
Vim really is an editor: It's designed around changing existing text. Inserting new text is just one of the actions you can perform, and you can combine that action with other modifiers, like "5ifoo<esc>" results in foofoofoofoofoo -- 5 repetitions of "insert foo"
This goes better when you know (and have internalized) more of the paths into insert mode.
For instance, ci} will delete everything inside the tightest enclosing braces and switch you to insert mode. This whole thing, then, including what you type, is a single action that you can redo with .
